It also appears that the secondary email is not looked at and is ignored. Also if you merge to leads and keep the business email and they come back with the personal email, a new lead is again created. There needs to be a solution to address it so that when two leads are merged, both email addresses are kept and looked at for tracking and used for sending communications etc...
This is something that we are currently evaluating and trying to come up with a best solution for, as we have issues with not just business and personal email addresses, but also multiple business email addresses and more. We want to retain both email addresses as records because they have unique email preferences, but also have a complete picture of everyone. I'd love to hear how anyone else has solved for this in SFDC or Marketo, although I feel like the best-practice solution will lie in SFDC since Marketo sees one email to one record.
My current SFDC solution that I have developed is this:
Create a new lead status of "Secondary Record". Place all leads that are not the primary record in the secondary record status.
I also created two new lookup fields. One is called "Primary Lead Record" and the other is "Primary Contact Record". Place these two fields on the lead layout and update them as needed.
This does not merge the lead/contact but does allow you to see/report what leads/contacts have a primary record.
The next issue is lead/contact activity. We want all lead activity to be kept in the primary record. I will create a new text area field for records called "Web Activity". I will also create a field that holds the date of the web activity updates (in Marketo and SF leads and SF contacts). Then I will compare the last updated time stamp of each record and if the last updated time of the secondary record activity is greater than the primary record I will append the secondary activity to the primary activity.
This will work with an unlimited number of relationships.
I am all open for better solutions.